North Korea offered "unconditional" talks with the South Wednesday, in its most conciliatory remarks since the nuclear-armed state sent tensions on the peninsula soaring by shelling a South Korean island.

In an unusually cordial statement, carried by its KCNA agency, North Korea said the communist nation "courteously proposes having wide-ranging dialogue and negotiations."

Pyongyang is "ready to meet anyone anytime anywhere", it said, calling for "unconditional and early opening of talks" among officials with "real power and responsibility."

The remarks were out of character for the reclusive regime led by Kim Jong-il, which regularly issues diatribes condemning Seoul as a puppet of the warmongering US.

But South Korean officials were dismissive of the comments. "What's more important is sincerity in North Korea's attitude," an unnamed official from Seoul's unification ministry, which handles relations with the North, told Yonhap news agency.

South Korea has regularly stressed that progress depends on the North's actions, rather than its words.

As well as the artillery strike, Pyongyang has also heightened security fears by disclosing a uranium enrichment plant, which specialists say could be used to develop materials for atomic weapons, to visiting US nuclear experts.

Washington echoed Seoul's response, saying that the North had to take "useful steps" to show that its proposal was serious.

"It needs to demonstrate it is sincere in the offer," State Department spokesman Philip Crowley told reporters, noting US Secretary of State Hillary Clinton discussed the plan with visiting Chinese Foreign Minister Yang Jiechi.

"There are still things that North Korea has to do to demonstrate a seriousness of purpose," Crowley said, such as ending its provocative behaviour, recommitting itself to a 2005 declaration for nuclear disarmament, and taking responsibility for sinking a South Korean warship last year.

Pyongyang's statement said that negotiations could not be conducted when the North and the South were engaged in "mud-slinging and provocative acts" against each other.

"In order to mend the north-south relations now at the lowest ebb we will conduct positive dialogue and negotiations," it added.

Analysts in Seoul were cautious. "North Korea appears to be making a bold proposal, although its sincerity has yet to be verified," said Kim Yong-Hyun, a professor at Seoul's Dongguk University.

The gesture came two days after South Korean President Lee Myung-Bak offered closer economic ties if it changes its course, amid a heightened diplomatic focus on the region over fears events on the peninsula could spiral out of control.

In his New Year policy address, delivered after the North had called for improved relations in 2011, Lee said the door for talks was "still open" if North Korea showed sincerity to mend ties.

Relations between the two Koreas were stretched to breaking point after the North shelled a South Korean island on the disputed border on November 23, killing four people, including two civilians.

The South has since staged a series of military exercises, including a live-fire drill on December 20 on the island, which again raised tensions but the North did not follow through with threats of a new and deadlier attack.

The top US envoy on North Korea landed in Beijing Wednesday for talks with Chinese officials, after a visit to Seoul focused on reducing frictions on the peninsula.

Stephen Bosworth was expected to head for Tokyo Thursday on a three-nation tour, while US Defence Secretary Robert Gates is also scheduled to meet his Chinese counterpart in a visit to Beijing starting January 9.

In Seoul, Bosworth met South Korea's chief nuclear negotiator, Wi Sung-lac, and Foreign Minister Kim Sung-Hwan.

Foreign ministry officials said Bosworth stressed Pyongyang needed to show it was sincere about mending ties with Seoul if six-party international talks on its nuclear programme were to resume.

The North has refused to discuss the nuclear issue directly with the South, saying it only wants to deal with Washington, but its latest statement suggests it may be willing to engage with Seoul on the topic.

Pyongyang has insisted its uranium plant is designed solely to fuel a light-water reactor being built to produce energy. But US officials and experts say this could easily be converted to produce weapons-grade uranium.